In deep sour gas wells oil may be pumped down the annulus between the well casing and the production tubing in order to prevent sulfur deposition and to carry oil-soluble corrosion inhibitors. Alternatively, oil may be injected into surface gathering lines to prevent sulfur deposition. The oil flows back up through the production tubing along with the produced gases, is separated from the gases at the gas plant, and recycled back to the wells (U.S. Pat. No. 3,393,733). As the oil circulates, it absorbs the small amounts of elemental sulfur, which are often produced by the wells. Since the oil is recirculated, there is a continuous increase in sulfur concentration. In order to operate over long periods of time, it is necessary to control the sulfur concentration by removing it from the oil as fast as it is added. Use of an alkali sulfide solution to extract sulfur (U.S. Pat. No. 3,474,028) is incompatible with the use of high molecular weight organic corrosion inhibitors due to the formation of stable oil/water emulsions. Accordingly, as more particularly described hereinafter, the present invention provides an alternate process for removal of sulfur from the circulating oil.
A patent of some pertinence to the present invention, U.S. Pat. No. 3,826,811 to Hakka, also relates to a process for inhibiting sulfur deposits in hydrocarbon gas wells. However, the invention of this patent is limited to directly contacting the hydrocarbon gas with an aqueous solution of monoethanolamine, dissolving the sulfur in the solution, and separating the solution from the hydrocarbon gas. By contrast, in the present invention a circulating oil removes the sulfur from the gas and an organic amine is employed to remove the sulfur from the circulating oil. Separation of the organic amine and circulating oil is substantially complete in the present invention, and there is sufficient water in the oil so that trace quantities of organic amine which remain in the oil comprise less than 5% by weight of the organic amine and water as required as a lower concentration limit in the Hakka patent.
A second pertinent patent, U.S. Pat. No. 2,890,931 to McCreary, pertains to the treatment of natural gas with aqueous monoethanolamine to remove sulfur impurities and regenerating the monoethanolamine by steam stripping. By comparison, the present invention employs C0.sub.2 to precipitate sulfur from the aqueous organic amine solution. While heat may be employed in the present invention to strip out the C0.sub.2, the heating is by indirect heat exchange and does not involve direct steam contact as in the McCreary process.